The reasons for the deactivation of the emergency shutdown system on the port main engine are still undetermined. There was considerable turnover among the engine-room staff, which compromised continuity in maintenance. The electrical shutdown system had been disconnected, but none of the engineers on duty at the time of the failure knew when or by whom it had been deactivated.Analysis The reasons for the deactivation of the emergency shutdown system on the port main engine are still undetermined. There was considerable turnover among the engine-room staff, which compromised continuity in maintenance. The electrical shutdown system had been disconnected, but none of the engineers on duty at the time of the failure knew when or by whom it had been deactivated. The nuts of the No.6 main bearing cap were not tightened properly when maintenance work was performed during the winter. Because of inadequate lubrication due to a drop in oil pressure, the No.4 piston seized up and damaged the bottom part of the cylinder liner. The damaged parts fell onto the crankshaft and were ejected with sufficient force that they passed through three crankcase doors. The emergency shutdown system on the port main engine had been deactivated for reasons as yet unknown. The smoke observed in the engine-room was in fact a haze of oil.Findings The nuts of the No.6 main bearing cap were not tightened properly when maintenance work was performed during the winter. Because of inadequate lubrication due to a drop in oil pressure, the No.4 piston seized up and damaged the bottom part of the cylinder liner. The damaged parts fell onto the crankshaft and were ejected with sufficient force that they passed through three crankcase doors. The emergency shutdown system on the port main engine had been deactivated for reasons as yet unknown. The smoke observed in the engine-room was in fact a haze of oil. The mechanical failure of the port engine of the ALGOWEST was caused by inadequate lubrication of the No.4 piston. Loose nuts allowed the No.6 main bearing cap to leak a quantity of oil intended to lubricate the damaged piston. The port engine did not shut down when the lubricating oil pressure dropped because the emergency shutdown system had been deactivated.Causes and Contributing Factors The mechanical failure of the port engine of the ALGOWEST was caused by inadequate lubrication of the No.4 piston. Loose nuts allowed the No.6 main bearing cap to leak a quantity of oil intended to lubricate the damaged piston. The port engine did not shut down when the lubricating oil pressure dropped because the emergency shutdown system had been deactivated. Following this occurrence, the owners/operators have reinforced the operating procedures for their fleet. The procedures now require the final tightening of all major engine components to be witnessed and recorded by the chief engineer. In addition, the procedure for handing over responsibility of work in hand has also been strengthened.Safety Action Taken Following this occurrence, the owners/operators have reinforced the operating procedures for their fleet. The procedures now require the final tightening of all major engine components to be witnessed and recorded by the chief engineer. In addition, the procedure for handing over responsibility of work in hand has also been strengthened.